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    <title>Document</title>
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    <script>
        //1.变量不可以重复声明
        let a =  9;
        let b,c,d;

        {
            //2.块级作用域、全局作用域、函数、eval
            let a = 'iloveyou'
            console.log(a)
        }
        console.log(a)

        
        //3.不存在变量提升：不允许变量在使用之前去使用变量
 
        console.log(aaa)    /* undefine */
        let aaa = 'dasfadf'



        //4.不影响作用域链
        {
            let schoole = 'jxlgdx';
            function show(){
                console.log(schoole)
            }
        }
        show();


    </script>





    
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